In current orthopaedic practice it is known to provide metal orthopaedic implants to repair or reconstruct joint movement for a patient. These metal orthopaedic implants are commonly made from cobalt chrome, titanium and stainless steel. Moreover, with cobalt chrome implants it is possible to provide a porous layer of cobalt chrome beads for intimate contact with bone to accommodate bone ingrowth into the porous layer. In a similar manner, titanium implants are provided with titanium beads or fiber metal pads in the form of a porous layer for bone ingrowth.
In contrast to the metal orthopaedic implants, U.S. Pat. No. 4,750,905, issued to James Koeneman et al on Jun. 14, 1988, teaches a composite hip prosthesis wherein nonmetallic components are assembled with a carbon fiber core, a woven fiber sheath and a thermoplastic resin skin forming the outer contour of a hip prosthesis.
A hybrid metallic/nonmetallic orthopaedic device is taught in U.S. Pat. No. 4,454,612, issued to John McDaniel on Jun. 19, 1984, wherein a metal core is covered with a thin polymer coating and a polymer fiber layer is attached to the coating to accommodate bone ingrowth.
One of the inventors of the present invention has proposed a substantially nonmetallic composite core with a porous metal surface embedded into the outer surface of the core to define a hybrid metallic/nonmetallic orthopaedic implant device. In U.S. Pat. No. 5,219,363 Roy Crowninshield, et al discloses a core made of fibers, a casing made from a polymer such as, polyetheretkerketone and a porous metal surface embedded into the outer surface of the polymer.
The aforegoing prior art addresses the issue of stress transfer in orthopaedic devices so that the interface between the orthopaedic device and the remaining bone does not impart substantially different loads to the remaining bone than ordinarily imparted prior to resection of bone. If the stress applied to the bone is not controlled excessive stresses may fracture the remaining bone stock while on the other hand stress shielding may result in bone resorption.